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Behavior of backreferences to named groups in regular expressions unclear #49132
Description
| BPO | 4882 |
|---|---|
| Nosy | @birkenfeld |
| Files |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = 'https://github.com/birkenfeld'
closed_at = <Date 2009-03-31.19:07:20.189>
created_at = <Date 2009-01-08.15:35:46.076>
labels = ['type-feature', 'docs']
title = 'Behavior of backreferences to named groups in regular expressions unclear'
updated_at = <Date 2009-03-31.19:07:20.188>
user = 'https://bugs.python.org/aresnick'bugs.python.org fields:
activity = <Date 2009-03-31.19:07:20.188>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = <Date 2009-03-31.19:07:20.189>
closer = 'georg.brandl'
components = ['Documentation']
creation = <Date 2009-01-08.15:35:46.076>
creator = 'aresnick'
dependencies = []
files = ['13016']
hgrepos = []
issue_num = 4882
keywords = ['patch']
message_count = 5.0
messages = ['79417', '79525', '80100', '81568', '84863']
nosy_count = 3.0
nosy_names = ['georg.brandl', 'jimjjewett', 'aresnick']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue4882'
versions = ['Python 2.6']
Activity
aresnick commentedon Jan 8, 2009
I recently learned about named groups in Python regular expressions.
Almost all the documentation I've found online explains what they are
and give a simple example of how to use them. I was trying to use the
variables outside of the original regex, later in the code. Nowhere in
the documentation I found after a couple hours of searching was it
mentioned that named groups can only be backreferenced _within_ the pattern.
In particular, the sections at
http://www.amk.ca/python/howto/regex/#SECTION000530000000000000000 and
the description of the (?P<name>) behavior at
http://docs.python.org/library/re.html could be modified to make it
clear that the named capture does not create a variable usable outside
of the pattern.
I would be happy to alter the documentation appropriately.
jimjjewett commentedon Jan 10, 2009
That sounds like a good idea, particularly since it is a bit different
from Perl. Please do write up the a clarification.
Typically, I have either attached a file with the suggested wording, or
included it in a comment from which a commiter could cut-and-paste.
(If Georg has different preferences on how to submit the patch, they
should probably go into a FAQ anyhow.)
birkenfeld commentedon Jan 18, 2009
I'm happy to review such a patch.
aresnick commentedon Feb 10, 2009
Hi Georg!
Sorry to be so long in getting back to you. I've attached a suggested
patch for the python-2.6.1-docs-text/library/re.txt documentation.
Also, in looking over Kuchling's HOWTO, the necessary information is
actually there, and I just wasn't paying attention =) Let me know if
I should do something else--this is my first 'fix'/submission to
Python, and I'm eager for feedback.
Thanks!
Gratefully,
a.
birkenfeld commentedon Mar 31, 2009
Committed a similar patch in r70866.